At present, there is considerable concern and debate about the possibility that environmental pollutants, through their effect on endocrine function, are responsible for reproductive and developmental abnormalities in various species including humans, it is also becoming increasingly clear that cellular signals mediated by endogenous hormones can be completely obscured or triggered by the presence of endocrine disrupting compounds (EDCs) which act as estrogen mimics or estrogen antagonists. Such perturbations during critical stages of fetal development can lead to abnormal and irreversible programming of developing organs and finally culminate in adult organ dysfunction or diseases. However, majority of the studies conducted thus far have failed to 1) utilize environmentally relevant low doses of EDCs and/or appropriate controls; 2) relate the selected doses to human exposure levels; and 3) take an indepth took at fetal exposures and its impact on reproductive competence as adult. The goal of this study is to expose sheep fetuses to environmentally relevant low concentrations of common xenoestrogens (bisphenol and methoxychlor) during critical stages of reproductive neuroendocrine system differentiation and to determine the impact of these pollutants on reproductive cyclicity and patterns of ovarian follicular distribution longitudinally. This study will utilize a well-characterized animal model for reproductive research with clearly identified developmental critical periods to target EDC treatment.